摘要:

A succession of two reactive chemical vapour depositions (RCVD) processes have been used to produce a double coating of TiC and SiC on a graphite substrate. In this paper, thermodynamic computations have been used to define the optimal conditions of the partial or the total conversion of a TiC coating into SiC. The experiments have been made on TiC powders and planar graphite substrates. The texture and the microstructure of the layers have been investigated as a function of the initial gas composition for different temperatures. These results will be useful to deposit a protective double layer on every single filament of a carbon fibre.

ISSN:0960-3409    

DOI:10.1080/09603409.1992.11689391

出版商:Taylor&Francis    

年代:1992

数据来源: Taylor

摘要:

Electrochemical investigation techniques (a.c. and d.c.) have been used to assess laboratory-simulated high-temperature fireside corrosion reactions. Tests have involved typical iron-base super-heater and reheater alloys subjected to molten salt corrosion in a combustion rig and a furnace-wall alloy subjected to dry oxidation/sulphidation conditions. The techniques have also been applied to a ceramic material, silicon carbide, exposed in a dry oxidation environment. Conclusions regarding corrosion rates estimated from the electrochemical data have been compared with those from metallographic examination of the test elements at the completion of the exposure tests. The results have shown that the ability of the electrochemical measurement techniques to evaluate the reaction processes is dependent on the ionic transport in the scale or in the deposits formed on the high- temperature surfaces during the combustion processes. Thus, dry oxidation/sulphidation of the alloys produces electronically conductive scales, while fluxing of the scales formed in thin-film molten salts results in a change from ionic to electronic conduction in the films; in both cases, electrochemical assessment of the corrosion reactions by using simple test cell configurations is prevented. However, the high ionic transport number of silicon oxide scales on silicon carbide allows measurement of charge-transfer resistances, which may be correlated with the reaction kinetics.

ISSN:0960-3409    

DOI:10.1080/09603409.1992.11689392

出版商:Taylor&Francis    

年代:1992

数据来源: Taylor

摘要:

It is a matter of common knowledge that in laboratory hot-dip aluminizing, great difficulties are often encountered in preparing specimens that are free of surface oxides and other ubiquitous contaminants such as oils, grease and dust. Inadequate preparation of specimens will inevitably lead to the prevention of alloy layer growth during hot dipping and poor coatings following withdrawal. This paper describes a method for the production on a laboratory scale of hot-dipped type 1 aluminized sheet- steel specimens of commercial quality.

ISSN:0960-3409    

DOI:10.1080/09603409.1992.11689393

出版商:Taylor&Francis    

年代:1992

数据来源: Taylor

摘要:

The oxidation behaviour of a number of iron/chromium/aluminium based oxide dispersion strengthened (ODS) alloys of the type MA 956 was investigated at temperatures between 900 and 1200°C. Apart from studies on long-time cyclic oxidation resistance, the main emphasis was placed on the effect of alloy yttria content on scale composition and structure as a function of time and temperature. The detailed scale analyses were made by using Rutherford backscattering analysis in addition to electron-optical methods. It was found that during short-term oxidation the scale growth rate at 900°C showed a deviation from the Arrhenius-type temperature dependence observed at higher temperatures. This could be attributed to formation of a metastable alumina modification in the initial stages of oxidation at 900°C. Studies of a series of alloys with variations of alloy yttria content in the range 0.17−0.7% showed an increase in the oxide growth rate with increasing yttria content. The reason for this technologically Important effect is discussed against the background of various studies on scale growth mechanisms.

ISSN:0960-3409    

DOI:10.1080/09603409.1992.11689394

出版商:Taylor&Francis    

年代:1992

数据来源: Taylor

摘要:

Three powder metallurgy (P/M) heats (two STAMPed and one HIPped) of 12 CrMoV steels have been creep tested and studied metallographically. At 550°C the creep strength of the P/M heats fell within the ISO scatterband for conventional 12% Cr steel. The HIPped heat had inferior creep properties, possibly due to a different heat treatment giving a coarser carbide distribution. At 600°C the only heat tested (STAMP) revealed a significantly higher creep strength than ISO data. The precipitates were mainly of type M23C6, but VN, NbC and intermetallic phases were also detected. The carbide coarsening during creep in P/M heats was found to be much slower than for a conventional steel, especially at 600°C, which explains the high creep strength at that temperature.

ISSN:0960-3409    

DOI:10.1080/09603409.1992.11689395

出版商:Taylor&Francis    

年代:1992

数据来源: Taylor

摘要:

The effect of boron and zirconium on the directional solidification behaviour and segregation of IN738 superalloy has been studied. It was found that additions of boron and zirconium enlarge the solidus-liquidus temperature interval and increase the amount of residual melt during solidification. Boron gives the alloy a tendency to form developed dendrites, while zirconium enhances a cellular solidified structure. Both boron and zirconium are shown to be rejected to the residual melt during solidification, and shown to change the segregation of alloying elements by interaction.

ISSN:0960-3409    

DOI:10.1080/09603409.1992.11689396

出版商:Taylor&Francis    

年代:1992

数据来源: Taylor

摘要:

The critical part of the transition metal joint between type 304 stainless steel and 2.25Cr-1Mo steel, with an immediate piece of Alloy 800, is the Alloy 800/2.25Cr-1Mo steel joint welded with Inconel 182. The performance of this trimetallic transition joint was studied by accelerated thermal cycling of the Alloy 800/2.25Cr-1Mo steel joint after subjecting it to its optimum post-weld heat treatment. The thermal cycling test procedure employed produces accelerated failures in transition metal joints similar to those observed in steam generators of operating power plants. The changes in the ferritic steel heat-affected zone on thermal cycling were also studied. The results of this study show that there is a marked improvement in performance, with at least a four-fold improvement in the life of the transition metal joint, on using the trimetallic configuration, instead of the direct (bimetallic) configuration.

ISSN:0960-3409    

DOI:10.1080/09603409.1992.11689397

出版商:Taylor&Francis    

年代:1992

数据来源: Taylor

摘要:

In this work, a fixed-bed gasifier was used to study the effects of some important parameters on both the temperature and the chemical composition of the off-gas produced in a CO2−O2coal gasification process. Also, the effect of these parameters on the gasification temperature was determined. The parameters tested included input-gas composition, coal rank, coal size and coal-bed depth. In addition, the reactivity of a sub-bituminous coal was investigated under different gasification temperatures. Gas chromatography was employed to analyse the chemical composition of the gases. The results indicated that the off-gas temperature increased with coal rank and decreased with both the CO2−O2ratio and the coal-bed depth. Generally, the amount of H2and CO in the off-gas decreased with both the coal rank and the CO2−O2ratio and increased with coal-bed depth. Coal size did not have a significant effect on the gasification process.

ISSN:0960-3409    

DOI:10.1080/09603409.1992.11689398

出版商:Taylor&Francis    

年代:1992

数据来源: Taylor

摘要:

The transformation characteristics of ferrite transformation in a cast of specially designed duplex stainless steel have been studied. The ferrite content in the duplex stainless steel was found to settle to steady values after long-term exposure to high temperatures. This feature can be used for developing an average temperature indicator that is very easy to use and requires only very simple equipment.

ISSN:0960-3409    

DOI:10.1080/09603409.1992.11689399

出版商:Taylor&Francis    

年代:1992

数据来源: Taylor

ISSN:0960-3409    

DOI:10.1080/09603409.1992.11689400

出版商:Taylor&Francis    

年代:1992

数据来源: Taylor